Transmission line formed by a dielectric body having a metallized nonplanar surface

ABSTRACT

A transmission line made of a block of dielectric material having a metallized formed surface which determines the electric and magnetic field characteristics of an electromagnetic wave applied thereto. The formed surface of the block of dielectric material is such as to define two sidewalls, a ridge between the two sidewalls and two bottom walls with the ridge being spaced between the sidewalls by the width of the bottom walls. The formed surface is covered by conductive material so as to cover the ridge, the bottom walls and the sidewalls, whereby the entire surface of the groove comprises conductive material. This transmission line lends itself to batch fabrication techniques for the production of a single transmission line or a complete system of such lines.

United States atent Cheng Paul Wen Trenton, NJ. [21] Appl. No. 850,862

[22] Filed Aug. 18, 1969 [45] Patented Dec. 21, I971 [73] Assignee RCA Corporation [72] Inventor [54] TRANSMISSION LINE FORMED BY A DIELECTRIC BODY HAVING A METAlLlLllZlElD NONPLANAR SURFACE 5 Claims, 6 Drawing Figs.

[52] 10.5. C1 3313/24.]1, 333/10, 333/95, 333/98 [51] Int. Cl 1101p 1/32, HOlp 3/12, HOlp 5/02 [50] Field of Search 333/95,

METALIZED-PLASTIC SYMMETRICAL TROUGH WAVEGUIDE w] mama Primary ExaminerH. K. Saalbach Assistant Examiner-Wm. I-I. Punter Almrney-Edward J. Norton ABSTRACT: A transmission line made of a block of dielectric material having a metallized formed surface which determines the electric and magnetic field characteristics of an electromagnetic wave applied thereto. The formed surface of the block of dielectric material is such as to define two sidewalls, a ridge between the two sidewalls and two bottom walls with the ridge being spaced between the sidewalls by the width of the bottom walls. The formed surface is covered by conductive material so as to cover the ridge, the bottom walls and the sidewalls, whereby the entire surface of the groove comprises conductive material. This transmission line lends itself to transmission line or a complete system: ofsuch lines.

FERRIMAGNETIC MATERIAL NONIVIAGNETIC PLASTIC FERRIMAGNETIC PLASTlC MIXTURE OR 4' FERROMAGNETIC PLASTIC l /HXTUE gig LATCHING WIRE AATENTED BEBE! 97K METALLIC FILM lilnlll. v AA A ll nllllllv.

METALlZED-PLASTIC 6 SYMMETRICAL THOUGH WAVEGUIDE ATTORNEY E E R R U U W m Mn M M 8 lfl C 9 U W/ S N. A A a DIRP IWOC m T M C T. PM E e E n 6% n L N A A C mm Gm l M Y MR AT m n W 8 M W E R m mm F m 2 '1 F T Q 4 5 4? 6%; Nu A E."

TRANSMISSION LINE FORMED BY A DIELECTRIC BODY HAVING A METALLIZED NONIPLANAIR SURFACE This invention relates to a formed transmission line structure and a method of making the structure which is particularly adaptable to batch fabrication techniques.

At the present time, considerable effort is being expended to develop microwave systems which operate at millimeter wavelengths. Transmission lines fabricated on dielectric substrates, such as strip transmission lines and microstrip transmission lines, suffer from high dielectric loss and the possibility of mode conversion or radiation unless their transverse or cross-sectional dimensions are substantially less than one-half wavelength. Because the transverse dimensions of the lines are small due to the operating wavelength, dielectric loading (which further shrinks these dimensions) becomes highly undesirable at high microwave frequencies.

Therefore, at millimeter wavelength, precision hollow waveguides are more desirable than strip transmission lines from the standpoint of loss. However, conventional hollow waveguides do not lend themselves to batch fabrication techniques, where such small dimensions are involved, and do not readily lend themselves to the coupling of circuit elements such as semiconductor diodes or ferrite elements to the waveguide structure.

Also, it is desirable to provide a structure in which a multiplicity of transmission lines coupled together to form a network may be produced in a single process which structure may conveniently accommodate various active and passive devices.

The present invention provides a new type of transmission line and a method of making this transmission line. This new type of transmission line is made up of a formed block of dielectric material having a configuration so as to provide a surface which, when covered by a conductive film, defines the modes and controls the field distribution of electromagnetic waves applied to the conductive surface.

' A more detailed description follows in conjunction with the following drawings wherein:

FIG. 1 is a perspective view of a trough waveguide in accordance with an embodiment of the present invention;

FIG. 2 is a perspective view of a trough waveguide illustrating the magnetic field vectors of electromagnetic waves traveling along the guide;

FIG. 3 is an end view ofa nonreciprocal trough waveguide device in accordance with another embodiment of the present invention;

FIG. 4 is an end view of a latching gyromagnetic trough waveguide device in accordance with a further embodiment of the present invention;

FIG. 5 is a trough waveguide coupler in accordance with still another embodiment of the present invention; and

FIG. 6 is an end view of a trough waveguide device using a permanent magnet as a part of the dielectric body.

Referring to FIG. 1 there is shown a perspective view of a new type of trough waveguide transmission line 10. A formed block ll of dielectric material such as any of the many wellknown plastics (polytertrafluoroethylene, polystyrene, polysuflone, for example) is formed so as to provide a deep slot or groove 13 which extends from one surface of the block 11 through a portion of the thickness of the block. This slot 13 is shaped to form a ridge 17 in the middle of the slot between and parallel to the formed sidewalls l9 and 21 of the groove 13. Also formed are bottom walls l8 and 12 between the respective sidewalls l9 and 21 and the ridge 17. A thin film of highly conductive material 23 such as gold, nickel, silver or copper is disposed on the surface of the ridge 17, on the bottom walls 18 and 12 and the sidewalls 19, 21 covering the groove 13 to present a type of unique trough waveguide. When the distance between the sidewalls l9 and 21 is less than one-half wavelength, the transverse electric (TE) mode is supported along the transmission line.

The method of manufacturing such a trough waveguide or system of trough waveguides utilizes the following steps. The

first step is to provide a master trough waveguide or a system of such waveguides, preferably by machining a brass trough waveguide as a master. From this master a mold or die having a shape complementary to that of the master is formed. A dielectric material such as a suitable plastic in liquid or solid form is then formed into the shape described above and shown in FIG. 1 by casting dielectric material. in a mold or by pressing the die against softened dielectric material which is sub sequently cured. Suitable plastics include polycarborates, polyacetals, polyurethanes, acrylics, polyesters, fluoracarbons, phenolics and epoxies. The soft dielectric material is then hardened either chemically or by heating. Alternatively, a thermoplastic material may be softened by heating, molded to the desired shape, and then cooled. A metal film of copper, gold, nickel, silver, etc., is then evaporated or electrolessly plated on the surfaces of the ridge sidewalls and bottom walls of the hardened dielectric block to provide the structure as shown in FIG. 1. If desired, the thickness of the evaporated or electrolessly plated metal film can be built up by electroplating a relatively thick metal film thereon. The remaining portion of the plastic block, which is not to be covered by conductive material, may be masked prior to forming the conductive surfaces on the sidewalls, bottom walls and the ridge of the groove.

In the example shown in FIG. 1, for a waveguide designed to operate in the X band frequency range, the width of the ridge is 50 mils, the width of the bottom walls or that between the sidewalls and ridge is mils wide. The ridge is 450 mils high and the sidewalls or depth of slot 13 extends another mils, or the total height of the sidewalls in 630 mils. In the construction of the trough waveguide structure in accordance with one example, a dielectric mold is made having a complimentary structure to that in FIG. l. The waveguide is molded by placing in the mold a liquid casting plastic. The liquid casting plastic used in the example is a material sold in a kit under the name of Castolite Liquid Casting Plastic by Castolite Com pany, Woodstock, Illinois, U.S.A. The kit includes a hardener which is used, after placing the liquid plastic in the mold, to harden the material. The surface portion of the plastic block where the slot is located is then plated so as to cover the sidewalls, ridge and bottom walls with electrolytic copper followed by a micron of gold.

Broadband impedance matching of a SO-ohm coaxial line to the line fabricated as described above has been achieved by placing the center conductor of the coaxial line on the ridge. The waveguide was operated in the frequency range of 8.0 to 12.0 GI-Iz. with better than 1.5 to 1 VSWR (voltage standing wave ratio); the total forward direction insertion loss was about 0.5 db.

The type of symmetrical trough waveguide shown in FIG. I may be considered as an analogue of a rectangular waveguide which has been opened lengthwise along the center of a broad wall and folded back upon itself with each half rotated 90. The magnetic vectors of a wave propagated along the guide are in the direction of the dashed arrows in FIG. 2. The magnetic vector of the RF (radiofrequency) signal is nearly circularly polarized one-half way down the slots or grooves, the sense of polarization depending on the direction of propagation of the signal.

Gyromagnetic material 31 through 34 (both ferromagnetic and ferrimagnetic material) such as ferrites and garnets may be placed halfway down the slot 13 in t the block Ill and between the ridge l7 and sidewalls l9 and Ill as shown in the cross-sectional views of FIG. 3. When a DC magnetic field of predetermined strength is applied to the materials 31-34 in the direction of arrow 30 perpendicular to the ridge, nonreciprocal gyromagnetic wave transmission devices are provided using this type of waveguide. Experimental results from a symmetrical trough ferrite isolator like that described above in connection with FIGS. 2 and 3 provided over 25.8 db. isolation accompanied by a 0.5 forward insertion loss at 10 GI-Iz. Four strips of Gl 13 (made by Trans-Tech, Gathersberg, Maryland, U.S.A.) ferrite rods, represented in the cross section of 31 through 34, (0.040 inch in diameter and 0.500 inch long) were attached to the conductor covered sidewalls of the slot 13 approximately one-half way up from the bottom walls 18 and 12 ofslot 13.

In like manner, a differential phase shifter may be provided with a similar configuration to that shown in FIGS. 1 and 3, with the strength of the DC magnetic field being either above or below the resonance value used when providing an isolator. For a differential phase shifter like that described above, the minimum differential phase shift was slightly over 85 with insertion loss in either direction less than 1 db. when operated over a frequency range of 9.2 GHZ. to 12.4 GHz.

Referring now to the arrangement shown in FIG. 4, a latching network is provided. Powders of gyromagnetic material (ferromagnetic and ferrimagnetic materials) are mixed into the dielectric body (made of liquid plastic for example) before casting the portion 41 of the body 45 of the trough waveguide. This gyromagnetic material is distributed throughout the body portion 41 and serves as part of the closed magnetic loop. Part of the closed magnetic loop is provided by ferrite sections 47 and 48 which bridge the gap between the ridge 51 and sidewalls 53 and 55 which are covered with a thin metallic film 60. A portion 43 of the ridge 51 comprises ferrite material; this portion 43 is adjacent the ferrite bars 47 and 48 of ferrite material. The remaining portion 63 of the ridge 51 comprises nonmagnetic dielectric material. A loop 67 is passed through, for example, an aperture 68 in the center of dielectric section 63 of ridge 51. Upon the application of a DC (direct current) pulse to loop 67, a closed magnetic path shown by dashed arrow lines is induced in the material which when the current is stopped the remanent magnetization provides the required DC magnetic field bias across the ferrite pieces 47 and 48.

The saturated magnetization of the ferrite and mixture in portions 41 and 43 is equal to the product of the saturation magnetization of the ferrite material employed and the fraction of the ferrite powder in the mixture by weight.

In the steps of manufacturing the structure illustrated in FIG. 4, separators may be used when molding to separate the ferrite plastic mixture from the nonmagnetic plastic material with the separator being inserted following the placement and hardening of the material just below.

The portion 41 of the dielectric body 45 in FIG. 4 may contain ferromagnetic materials. These ferromagnetic materials can provide a permanent magnet which is an integral part of portion 41 of dielectric body 45 and these materials can be poled so as to provide the desired magnetization.

A coupler similar to the top wall coupler between conventional waveguides can be provided as illustrated by the crosssectional configuration of FIG. 5. The opposed surfaces 71 and 73 of dielectric block 70 are formed as described above by molding, injection-molding or diecasting techniques. The grooved surfaces have opposed ridges 75 and 76 centered between the respective sidewalls 77 and 78, and 79 and 80. The bottom walls 81 and 82 of one surface 71 are opposed to the bottom walls 83 and 85 of the opposite surface 73. The block 70 has a pair of apertures 87 and 88 which extend entirely through the block 70 between the bottom walls 81 and 83 and the bottom walls 82 and 85. A thin conductive film covers the entire surface 71 and 73 except that portion where the apertures 87 and 88 are located. In operation, RF signals applied in one trough waveguide or along one surface 71, for example, are coupled to the opposite trough waveguide surface 73 through coupling apertures 87 and 88.

What is claimed is:

1. A transmission line, comprising:

a body of dielectric material having a grooved surface which defines two sidewalls, a ridge between said two sidewalls, and two bottom walls with the ridge being spaced between the sidewalls by the width of the bottom walls,

said body containing gyromagnetic material particles distributed throughout at least a portion of said body, and

a thin film of conductive material covering the ridge and the bottom and side walls whereby the entire surface of the groove comprises conductive material.

2. A trough waveguide comprising:

a body of dielectric material having a grooved surface which defines two sidewalls, a ridge between said two sidewalls and two bottom walls with the ridge being spaced between the sidewalls by the width of the bottom walls, said ridge, said bottom walls and said sidewalls being dimensioned and arranged such that said surface, when covered by conductive material, defines and controls the electric and magnetic field distribution of electromagnetic waves applied thereto, said body including a permanent magnet as an integral part thereof, and a thin film of conductive material covering said ridge, said bottom walls and said sidewalls whereby the entire surface of the groove comprises conductive material.

3. A nonreciprocal device, comprising:

a body of dielectric material having a groove formed in one surface in a manner to define two sidewalls, a ridge between said two sidewalls, and two bottom walls with the ridge spaced between the sidewalls by the width of the bottom walls,

a thin film of conductive material covering said one surface defining the ridge, the bottom wall and sidewalls whereby said surface defines the modes and controls the electromagnetic field distribution of an electromagnetic wave applied thereto, and

at least one slab of gyromagnetic material in said groove and extending between at least one sidewall and said ridge,

said body of dielectric material having portions adjacent said groove comprising gyromagnetic material so as "to form in cooperation with the slab of gyromagnetic material and said conductive film, a closed magnetic flux path loop, and

a latching wire passing through said closed loop.

4. The device as claimed in claim 3 wherein there are two slabs of gyromagnetic material each slab being coupled between one of said sidewalls and said ridge, the portion of said ridge at the coupled region also comprising gyromagnetic material.

5. An open trough waveguide coupler for operation over a selected range of frequencies comprising:

a block of dielectric material having a first grooved surface which defines two sidewalls spaced less than one-half wavelength apart at said selected frequencies, a ridge between the two sidewalls and two bottom walls of a first open trough waveguide,

said block of dielectric material having a second grooved surface symmetrically disposed opposite said first grooved surface, said second grooved surface defining two additional sidewalls spaced less than one-half wavelength apart at said selected frequencies, an additional ridge between said additional sidewalls and two ad ditional bottom walls of a second open trough waveguide,

said ridge, said bottom walls and said sidewalls of said first and second grooved surfaces being dimensioned and arranged such that each of said first and second surfaces when covered-by conductive material support a bound trough waveguide mode upon the application of electromagnetic waves thereto, said block of dielectric material having a first aperture which extends entirely through said block between a first of said bottom walls of said first trough waveguide and a corresponding additional bottom wall of said second trough waveguide,

said block of dielectric material having a second aperture which extends entirely through said block between a second of said bottom walls of said first trough waveguide and a corresponding additional bottom wall of said second trough waveguide,

a film of conductive material covering said first and second surfaces, I

said bound trough waveguide mode being excited in said first trough waveguide, and

means associated with said second trough waveguide for sensing coupled signal waves in the bound trough waveguide mode from said first trough waveguide. 

2. A trough waveguide comprising: a body of dielectric material having a grooved surface which defines two sidewalls, a ridge between said two sidewalls and two bottom walls with the ridge being spaced between the sidewalls by the width of the bottom walls, said ridge, said bottom walls and said sidewalls being dimensioned and arranged such that said surface, when covered by conductive material, defines and controls the electric and magnetic field distribution of electromagnetic waves applied thereto, said body including a permanent magnet as an integral part thereof, and a thin film of conductive material covering said ridge, said bottom walls and said sidewalls whereby the entire surface of the groove comprises conductive material.
 3. A nonreciprocal device, comprising: a body of dielectric material having a groove formed in one surface in a manner to define two sidewalls, a ridge between said two sidewalls, and two bottom walls with the ridge spaced between the sidewalls by the width of the bottom walls, a thin film of conductive material covering said one surface defining the ridge, the bottom wall and sidewalls whereby said surface defines the modes and controls the electromagnetic field distribution of an electromagnetic wave applied thereto, and at least one slab of gyromagnetic material in said groove and extending between at least one sidewall and Said ridge, said body of dielectric material having portions adjacent said groove comprising gyromagnetic material so as to form in cooperation with the slab of gyromagnetic material and said conductive film, a closed magnetic flux path loop, and a latching wire passing through said closed loop.
 4. The device as claimed in claim 3 wherein there are two slabs of gyromagnetic material each slab being coupled between one of said sidewalls and said ridge, the portion of said ridge at the coupled region also comprising gyromagnetic material.
 5. An open trough waveguide coupler for operation over a selected range of frequencies comprising: a block of dielectric material having a first grooved surface which defines two sidewalls spaced less than one-half wavelength apart at said selected frequencies, a ridge between the two sidewalls and two bottom walls of a first open trough waveguide, said block of dielectric material having a second grooved surface symmetrically disposed opposite said first grooved surface, said second grooved surface defining two additional sidewalls spaced less than one-half wavelength apart at said selected frequencies, an additional ridge between said additional sidewalls and two additional bottom walls of a second open trough waveguide, said ridge, said bottom walls and said sidewalls of said first and second grooved surfaces being dimensioned and arranged such that each of said first and second surfaces when covered by conductive material support a bound trough waveguide mode upon the application of electromagnetic waves thereto, said block of dielectric material having a first aperture which extends entirely through said block between a first of said bottom walls of said first trough waveguide and a corresponding additional bottom wall of said second trough waveguide, said block of dielectric material having a second aperture which extends entirely through said block between a second of said bottom walls of said first trough waveguide and a corresponding additional bottom wall of said second trough waveguide, a film of conductive material covering said first and second surfaces, said bound trough waveguide mode being excited in said first trough waveguide, and means associated with said second trough waveguide for sensing coupled signal waves in the bound trough waveguide mode from said first trough waveguide. 